1. Field of the Invention
The present invention relates to an alarm control method for detecting abnormality in a drive circuit of an actuator.
2. Description of the Related Art
In a serial printer, a space motor is driven to move a print head. A head drive circuit is controlled based on printing data transmitted from a host computer thereby to drive the print head. Upon completion of printing for one line, a line feed motor is driven to perform a line feed so that the printing in the succeeding line is performed.
The serial printer includes a print head, a space motor and a line feed motor respectively serving as an actuator. The serial printer also includes a print head drive circuit for driving the print head, a space motor drive circuit for driving the space motor and a line feed motor drive circuit for driving the line feed motor. These drive circuits are connected to an excitation coil. When a drive current is applied to the excitation coil to drive these actuators.
However, if transistors constituting parts of the drive circuits are broken by an external noise, abnormal current may flow through the excitation coil, or if the excitation coil per se is short-circuited, excessive current may flow in the drive circuits, whereby a fire may occur.
To prevent the fire from occurring, a power supply of the printer is cut off when an alarm signal is supplied by monitoring the current to be supplied to the excitation coil.
However, in the conventional method, an output of the alarm signal on the basis of a reference voltage comprises two kinds of signals, i.e. ON and OFF in which the complete destruction alone is communicated to an operator by the ON signal. That is, the alarm signal is not output in a slightly abnormal condition. Accordingly, it is difficult to detect the abnormal condition and cope with it in early stages.